Visual acuity (VA) is the most commonly-used measure of human visual function, and is considered the standard measure of visual function in clinical settings. Standard tests of VA measure the ability to identify black symbols on a white background at a standardized distance as a function of the size of the symbols, such as with one of the familiar eye charts (e.g., Snellen, Bailey-Lovie, Tumbling E, Landolt C, and so forth) at a standardized distance of approximately 6 meters or 20 feet. A person with standard (normal) VA can recognize a letter or a symbol that subtends an angle of 5 arc minutes. The block letter E, for example, has three horizontal black strokes plus two interspersed horizontal white spaces of comparable thickness, meaning that normal human visual resolution is nominally one (1) arc minute. For angular values of this magnitude, the angle subtended by an object is approximately inversely proportional to distance.
Clinically, a level of VA specified as 6/6 (meters) or 20/20 (feet) is considered good normal vision. An alternative clinical measure of VA is expressed as the Logarithm of the Minimum Angle of Resolution (LogMAR), where 6/6 or 20/20 has a LogMAR VA measure of 0.0; 6/60 or 20/200 has a LogMAR VA measure of 1.0; and 6/3 or 20/10 has a LogMAR VA measure of −0.3). Measures of VA herein also include a measure of the ability to see a given object size at a given duration of exposure and/or at a given contrast level.
There are drawbacks to directly measuring VA as described above. Typically VA must be measured via an eye chart with the aid of clinician, who instructs the subject to read a specific line of the eye chart and then evaluates the subject's response. In addition, there are cases for which the VA falls within the range of normal vision even in the presence of severe visual problems and eye diseases, such as glaucoma or early retinopathy.
Thus, it would be useful and desirable to have alternative or complementary visual testing methods for clinical and research use, which achieve a high degree of correlation with the eye chart, but which can be administered without the need for a clinician, and which have the potential to detect visual pathologies. This goal is met by embodiments of the present invention.
Attention-Deficit Hyperactivity Disorder (ADHD) is a common neurobehavioral disorder that impairs the quality of life in both children and adults. The main symptoms include inattentiveness, hyperactivity and impulsivity. ADHD is usually diagnosed in childhood and often lasts into adulthood. Currently there is no simple objective diagnostic or screening test for ADHD. ADHD is diagnosed by clinicians in a several step process, using highly subjective tools, such as questionnaires, sometimes supported by computerized tests (T.O.V.A., MOXO). In children in particular, the diagnosis is confounded by parent's subjective input and child's general intelligence level. Accordingly there is a further need for an accessible screening tool that can assist adults with ADHD symptoms and parents to decide whether to seek clinical assessment.